1. Field of the Invention
The invention relates to CDMA telecommunications systems and methods and receivers employed therein for power estimation.
2. Description of the Related Art
In CDMA (Code Division Multiple Access) telecommunications systems estimation of received power is important, for instance, in power control and handover decisions. Estimation of an average signal power is important in the optimal adjustment of system parameters. The signal power estimation is also important in view of the handover algorithm.
Particularly in environments, where rapid, impulsive interferences, resulting from multipath propagation, for instance, affect the quality of a received signal, it is important to estimate the power accurately. Impulses disturb the methods used for power estimation, and consequently, the power estimation may fail. The power estimation algorithms used in the CDMA telecommunications systems try to filter off fast impulses from the received signal, and ideally they should be simple.
It has become more and more common to use so-called robust, i.e. control-weighted methods for eliminating impulsive interference in the telecommunications systems. The robust methods are not sensitive to big changes in individual observation values, such as impulse-like interference in a received signal. The prior art robust methods utilize so-called order statistics, the basic idea of which is to detect and eliminate observed interference by properties associated with an observation set arranged on the basis of variable values. One prior art robust method is so-called median-type filtering. This kind of prior art median-type filtering, used for power estimation, is described in greater detail, for instance, in the publication by C. Tepedelenlio{hacek over (g)}lu, N. Sidiropoulos, G. B. Giannakis, “Median Filtering For Power Estimation In Mobile Communication Systems”, Third IEEE Signal Processing Workshop on Signal Processing Advances in Wireless Communications, Taoyuan, Taiwan, Mar. 20–23, 2001, pp 229–231.
The prior art solutions have a drawback that advance information on an interfering signal is required in order that correct interference impulses could be detected. The prior art solutions do not operate well at high impulse interference frequencies, so they are not very efficient computationally. In addition, the prior art solutions are difficult to implement in practice.